Cart session.

Cart session id can be transferred via non-secure connection. So the cart session id must be changed when a customer try to make an order.

It is expected to lock cart when customer begins to make an order. And if cart is updated, cart will be unlocked every time. Then, while ordering, CGI should check whether cart is locked or not. If it is not locked, it should stop ordering process.

Column	Type	Constraint	Description
shop	TEXT	PRIMARY KEY	Shop ID. (shop.username)
session_id	TEXT		Cart session id. Random string.
cart_id	INTEGER	NOT NULL	Cart ID. (cart.id)
locked	INTEGER	NOT NULL	Cart is locked or not. 0: Un-locked 1: Locked

CREATE TABLE cart_session(
shop           TEXT,
session_id     TEXT,
cart_id        INTEGER  NOT NULL,
locked         INTEGER  NOT NULL,
PRIMARY KEY(shop, session_id)
);